The use of activated carbon for purifying liquids or gases is generally known in the art. A detailed description is rendered in the book of H. von Kienle and E. Bader "Aktivokhle und ihre industrielle Anwendung", Ferdinand Enke Verlag, Stuttgart 1980.
The use of pulverulent activated carbon is not possible for many purposes so that one has to switch over to die-pressed or molded carbon (Formkohle). the use in the form of blanks, for example, for pharmaceutical purposes, is of secondary importance.
Molded carbon is characterized by high activity and good hardness. Its regular, often rod-shaped configuration is particularly advantageous for use in charging filters.
Molded or shaped carbon is, for example, manufactured from ground pit coal and a pitch binder. The mixture is pressed to strands by means of an extruder, if desired, cut down, and the so-obtained sausage-shaped articles or cylinders are then smouldered, i.e. carbonized, and activated. Limits are set by the process technology as to the minimum dimension, which is in the range of approximately one millimeter.
Other methods are applied for producing spherical particles, in particular microspherules. For example, a dispersion is prepared from bitumen under pressure, above its softening point, in a medium which is not miscible therewith, such as water, said dispersion being quenched, the so-obtained bitumen spherules extracted with a suitable solvent, oxidized, carbonized and finally activated.
An alternative method for preparing carbonized carbon spherules from bitumen consists in spraying molten bitumen to obtain the desired droplet size and feeding these droplets together with an inert gas through a zone heated to between 800.degree. C. and 1600.degree. C. By virtue of this treatment, first the outer layer of the droplets is carbonized and thereafter the interior surface of the bitumen.
The activated carbon spherules thus produced have a hard shell and a somewhat softer core. For instance, spherule diameters of from 0.1 to 1 mm, with a relatively large size distribution. The abrasion resistance is very high by virtue of the particularly hard core. The inner surface amounts to approximately 600 to 1500 m.sup.2 /g, with a relatively high component of mesopores (10-15.times.10.sup.-10 m).
Another possibility of producing activated carbon spherules comprises heating organic cation exchangers in a fluidized bed rapidly to 600.degree.-700.degree. C. and thereafter activating the same, for example, with water vapor. The strength of the resulting absorber spherules is satisfactory for most applications, although it is a little lower than that of the material prepared from bitumen.